Diode Test (On Vehicle)

Disconnect electric choke (if equipped) and voltage regulator plug. Connect jumper wire between "A" and "F" terminals of voltage regulator wiring plug. Connect voltmeter to battery posts, start and run engine at idle speed, then record voltmeter reading. Move positive voltmeter lead to "S" terminal in regulator wiring plug and note voltmeter reading. If meter reads 1/2 of battery voltage, diodes are in working order. If meter reads approximately 1.5 volts, alternator has shorted negative diode or grounded stator winding. If meter reads approximately 1.5 volts less than battery voltage, alternator has shorted positive diode. If meter reading is 1.0-1.5 volts less than 1/2 battery voltage, alternator has an open positive diode. Reconnect electric choke (if equipped) back into circuit after test is completed.